The influence of acid etching on the electrochemical supercapacitive properties of NiP coatings

Amorphous NiP coatings were deposited onto Ti substrates using the electroless method and subsequently etched with nitric acid at different concentrations. Such coatings were employed as a potential electrode for a supercapacitor, with the results indicating that these electrodes exhibited high specific capacitance by controlling the etching conditions, including acid concentration and etching time. Dealloying by acid etching can significantly improve the supercapacitive performance of NiP coatings. The specific capacitance increased 40-fold and achieved levels as high as 865 F g− 1 at 10 mV s− 1 and 1254 F g− 1 at 1 A g− 1. This is mainly ascribed to the formation of porous structures and thus an increase of surface area due to Ni dissolving in acid solution. According to impedance analysis, the etching step can decrease the charge transfer resistance and Warburg impedance, thus improving the pseudocapacitive property. Moreover, the etched NiP coatings exhibit good cycling performance, and there is no noticeable specific capacitance decrement observed after 500 CV cycles at a scan rate of 10 mV s− 1. Specifically, such electrodes also have low reflectivity, as low as 0.4%.